Field of the Disclosure
The present disclosure relates generally to a system and method for an elevator safety mechanism and, more particularly, to a system and method for a governor inertia carrier used in activating an elevator safety mechanism.
Description of Related Art
In various elevator installations, a safety mechanism is installed on an elevator car to bring the descending elevator car to a stop under certain conditions, such as an uncontrolled descending of the elevator car. The safety mechanism, when actuated, typically operates upon guide rails between which the elevator car is located. The safety mechanism is actuated by a separate speed governor which is set to trip at a predetermined car speed in the down travel direction.
With reference to FIG. 1, an elevator installation equipped with a safety mechanism is shown according to the known state of the art. This installation has an elevator car 10 which is moved between different floors of an elevator shaft (not shown), for example by means of a motor 20 acting on a traction cable or a cluster of traction cables 21. One end of the traction cable or cluster of traction cables 21 is connected to the elevator car 10, while the opposing end of the traction cable or cluster of traction cables 21 is connected to a counterweight 22. The elevator car 10 is guided by a pair of lateral rails 30 extending vertically in the elevator shaft. The elevator car 10 engages the rails 30 through guides 31. For clarity, only one of these rails 30 is shown in FIG. 1.
The elevator installation has a governor assembly having a governor sheave 50 which is mounted in a top potion of the elevator shaft and a governor cable 60 wound between the governor sheave 50 and a tail sheave 51. The governor cable 60 is tensioned by means of a tension weight 52 acting on the tail sheave 51.
The governor cable 60 is fixed to the elevator car 10 by a plate 53, which is also connected to a safety mechanism 15 mounted on the elevator car 10 by a governor rope lever 11. In normal operation, such as when the speed of the elevator car 10 is less than a limit speed, the elevator car 10 drives the governor cable 60. Such movement of the governor cable 60 rotates the governor sheave 50. During normal operation, any stress on the plate 53 by a pulling force due to the inertia of the governor cable 60 may be offset by, for example, one or more holding tension springs.
When the speed of the car 10 reaches or exceeds a limit speed by at least a predetermined amount, such as when the car 10 starts to free fall, the governor sheave 50 locks, such as by actuation of centrifugal weights that engage a toothed fixed cylinder, and the governor cable 60 is immobilized. This causes a pulling force on the plate 53, which actuates the governor rope lever 11, which then acts on the safety mechanism 15 to actuate brakes 12 and 13. The brakes 12, 13, in return, engage the rails 30, such as by clamping against the rails 30, to bring the elevator car 10 to a safe stop.
One of the drawbacks of existing safety mechanisms is that inertia of the governor assembly during normal operation can cause unintended activation of the safety mechanism. During normal acceleration of the elevator car, the inertia of the governor rope 60, the sheaves 50, 51, and the tension weight 52 exerts a force on the governor rope lever 11. In certain circumstances, the inertia of the governor assembly can activate the safety assembly even though the elevator car 10 is operated within the limit speed. One solution to this problem is to use one or more holding tension springs to hold a safety arm connected to the governor rope lever 11 and prevent its unintended engagement until the limit speed is reached or exceeded. However, space surrounding the safety mechanism 15 is critical, and multiple tension springs often require more space than what is available. In addition, the force exerted by the springs increases linearly as the safety mechanism is activated, thereby resulting in large activation forces on various components and linkages of the safety assembly.
It would be desirable to provide a new and improved safety mechanism for preventing unintended activation of the safety mechanism due to inertia of the governor assembly.